1. Field of the Invention
The present invention relates generally to molecular pharmacology and therapeutics of lysosomal storage diseases. More specifically, the present invention relates to methods of using aminoglycoside antibiotics to treat mucopolysaccharidosis I (particularly Hurler Syndrome) and Batten disease.
2. Description of the Related Art
The lysosome is the cellular compartment that facilitates the degradation of macromolecules in the cell that have outlived their usefulness to the cell. Because of this important degradative role, many hydrolytic enzymes required to carry out the destruction of these surplus macromolecules reside in the lysosome. When one or more of these enzymes is missing, their substrates can no longer be degraded and accumulate, leading to a series of disorders that are frequently referred to as lysosomal storage diseases.
The term mucopolysaccharidoses describes a class of lysosomal storage disorders that are characterized by the excessive accumulation of glycosaminoglycans (GAGs) within the lysosomes of various tissues. Among these disorders, mucopolysaccharidosis I (MPS I) is an autosomal recessive lysosomal storage disease caused by a loss of the enzyme α-L-iduronidase, which participates in the degradation of glycosaminoglycans within the lysosome. Mucopolysaccharidosis I can be further subdivided into three categories: Hurler (MPS I-H), the most severe form; Scheie (MPS I-S) a mild form; and Hurler/Scheie (MPS I-H/S), an intermediate form. Hurler syndrome is characterized by a near total absence of α-L-iduronidase activity, leading to the accumulation of both dermatan and heparan sulfate within the lysosomes (6). Physical symptoms of the disease include stiffness in joints, skeletal abnormalities and corneal clouding. Progression of Hurler syndrome results in heart and liver disease as well as mental deterioration, with death usually occurring in childhood (7).
The two most frequent mutations found in MPS I patients with Hurler syndrome, the Q70X and W402X nonsense mutations, are present in ˜70% of patients of European descent (8). Significantly, the other forms of MPS I present clinically with milder symptoms, suggesting that much of the disease phenotype can be alleviated by as little as 1% of normal α-L-iduronidase activity (9-11).
Another group of lysosomal storage diseases which may benefit from the novel use of aminoglycosides for suppression therapy are the neuronal ceroid lipofuscinoses (NCLs), also collectively known as Batten disease. The neuronal ceroid lipofuscinoses are the most common childhood neurodegenerative disease with an incidence of 1 in 100,000. All types of neuronal ceroid lipofuscinoses are inherited in an autosomal recessive manner. Symptoms of neuronal ceroid lipofuscinoses include visual loss, seizures, paralysis, dementia, and premature death. The neuronal ceroid lipofuscinoses can be subdivided into four major types based upon the age of onset: infantile, late infantile, juvenile, and adult. In addition, the type of accumulating material within the lysosomes varies among the different forms of neuronal ceroid lipofuscinosis. Specifically, at least eight genes underlie the neuronal ceroid lipofuscinoses, four of which have been isolated and the mutations that cause neuronal ceroid lipofuscinosis characterized. These include CLN1, CLN2, CLN3, and CLN5. Mutations in CLN2 are associated with the late infantile onset form of neuronal ceroid lipofuscinosis. CLN2 has been found to contain the most nonsense mutations among the NCLs (26% of the characterized alleles)[Hum. Mut. 14: 199-215, 1999]. The protein encoded by CLN2 is tripeptidyl-peptidase I (TTP1) which functions in degradation of proteins within the lysosome. Without this enzyme, selected proteins accumulate within the lysosomes, with the major component of the accumulation products being an extremely hydrophobic subunit of the mitochondrial ATP synthase. The lysosomal accumulation of this type of storage product causes the onset of the late infantile form of neuronal ceroid lipofuscinosis. [Biochim. Biophys. Acta 1429: 496-500, 1999; J. Neurochem. 72: 2573-2582, 1999]. Aminoglycosides will be utilized to suppress premature stop mutations within the CLN2 gene in order to restore sufficient levels of TTP1, and alleviate the disease phenotype. This approach may be used prior to or contemporaneously with treatment consisting of the administration of recombinantly produced TTP1 and/or a CLN2 gene therapy vector [J. Neurochem. 73: 700-711, 1999].
Other studies have shown that aminoglycosides can also suppress premature stop mutations in other non-lysosomal diseases at levels that restore physiologically relevant amounts of functional protein. The utility of this approach was first demonstrated with the autosomal recessive disease cystic fibrosis (CF), where the aminoglycosides gentamicin and G418 were shown to suppress nonsense mutations in the CF-transmembrane conductance regulator (CFTR) gene (1,2). These compounds were shown to suppress a genomic cystic fibrosis nonsense mutation in a human bronchial epithelial cell line, restoring both CFTR protein localized to the apical plasma membrane and its cAMP-activated chloride channel activity. The specificity of aminoglycoside action for nonsense suppression was shown in these studies since cells homozygous for the ΔF508 CFTR allele did not respond to aminoglycoside treatment. More recently, clinical data obtained in pilot studies with cystic fibrosis patients carrying nonsense mutations indicated that topical or intravenous gentamicin can partially restore CFTR activity in vivo (3,4). Another study found that gentamicin can also suppress a nonsense mutation in the dystrophin (Dmd) gene of the mdx mouse, which represents an animal model for Duchenne muscular dystrophy (5). The partial restoration of dystrophin expression was accompanied by a significant decrease in muscular deterioration in treated animals. However, the ability of aminoglycosides to suppress stop mutations and reverse the biochemical defects associated with any other human genetic disease is highly unpredictable.
The well-defined correlation between enzymatic activity and disease severity makes the MPS I and NCL disorders good candidate diseases to examine whether the level of protein expression restored by aminoglycoside suppression of stop mutations can reverse the biochemical defects associated with a human genetic disease.
The prior art is deficient in an effective therapeutic regimen for either MPS I (such as Hurler syndrome) or the neuronal ceroid lipofuscinoses (such as Batten disease). The present fulfills this long-standing need and desire in the art to provide a treatment for these lysosomal storage diseases.